Resources

A Closer look at…. Powerline engineering

Posted
February 20 2018

Highly experienced Powerline Engineer, Tola Aina, talks about some of the different engineering services provided by NM Group. He explains how varying types of projects might be tackled and the benefit provided to the client.

“There are two key objectives in everything that we do; reliability and utilisation. We safeguard the line and then ensure it is transferring as much power as possible. Remediation is maintaining the line as it is, fixing any identified constraints to achieve a particular thermal rating. Up-rating is increasing the capacity to transfer more load along the line. Remediation increases reliability, and uprating utilisation. Population and energy demand is growing and increasing utilisation helps to meet that demand without the need for new lines.

Looking at remediation first. We run a thermal rating on the line and find out where the constraints are. There will be spans that are limited because of clearance issues. An example might be if there is a crossing of two different voltage lines and the lower line passes under too close, that is a constraint. This means that the span can’t get to the desired rating, because the infringement might mean that conductor clashing takes place with the line below. We would run the analysis in PLS-CADD™ and make recommendations to fix any constraints identified.

So to take this example, you can lower the line if it will still meet statutory requirements or you can cable the line i.e. put it underground. Then you won’t have any clearance issues for your crossing and the constraint is gone. Another method is to offset tension on the span concerned. When you do analysis on the line you can state that the span is cut off at a particular point, (such as taking 100mm off the cable). Sag and tension are inversely related and tensioning gives you more clearance below the line allowing you to run it at the desired rating.

“There are two key objectives in everything that we do; reliability and utilisation. We safeguard the line and then ensure it is transferring as much power as possible.”

That’s just two examples of remediation. If a span is infringing to ground, I might suggest that they retension the cable or excavate the ground below the line in some cases. Or there might be a car park or temporary building that can be moved. A few years back, a farm had stacked bales of hay beneath the line and that was identified as an infringement. All they needed to do to resolve it was move the bales of hay. It’s not a classic engineering solution, but was a very quick and easy fix! If we hadn’t captured imagery alongside LiDAR data during the aerial survey, we wouldn’t have seen that.

On to Up-rating. To increase the transfer capacity of a line, the easiest design method is to re-conductor it or change the conductor along the length of the circuit to a High Thermal Low Sag (HTLS) conductor. This means it doesn’t sag as much when temperature is higher due to increased load. Using PLS-CADD™ and PLS Tower™ analysis, you need to check the structural strength of the towers to ensure that they can support the new conductor.

Although often the most efficient, re-conductoring is the most expensive option. Many of the spans will not have constraints. So replacing the line with new conductor will have no benefit to these spans. Therefore, it is not always the best option to re-conductor the line. Re-conductoring is a cost benefit or engineering judgement call. To achieve up-rating, it is sometimes more appropriate to employ remediation. Remediation isn’t just a technique to manage failing lines. You can do little things, which make a massive difference to the potential thermal rating of the line."